major reference

The large-scale use of such ionizing radiation for modifying and synthesizing materials, known as
radiation processing, represents a minor yet significant technology. It involves irradiating materials either with a beam of electrons produced by a high-voltage particle accelerator or with gamma rays emitted by the radioisotope cobalt-16 or, in a few cases, cesium-137. The electrons are generally...

use in gemstones

Irradiation of certain gemstones also causes colour changes. Some colourless diamonds become green, rose quartz becomes brown, and decolourized amethyst regains its purple hue. These colour changes are not always permanent, and the stone may become radioactive.